Modulating system



July 17, 1923. 1,462,038

R. v` l.. HARTLEY MODULATING SYSTEM Original Filed Dec. 30, 1916y 2Sheets-Sheet l July 17, 1923. 1,462,038

R. v. L.. HARTLEY MODULATING SYSTEM Original Filed Deo. 30, 1916 2Sheets-Sheet 2 frequency Patented July 17. 1923.

UNITED STATES RALPH V. L. HARTLEY, OF SOUTH ORAN GE, NEW JERSEY,ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y.,A CORPORATION OIF NEW YORK.

MODULATING SYSTEM.

Application led December 30, 1916, Serial No. 139,784. Renewed October25, 1922. Serial No. 596,899. l

To all whom 'it may concern.:

Be it known that I, RALPH V. L. HARTLEY, a citizen of the United States,residing at South Orange, in the county of Essex and State of NewJersey, haveinvented certain new and useful Improvements in ModulatingSystems, of which the following is a full, clear, concise, and exactdescription.

The invention relates to modulating systems, or systems for supplying ahigh frequenc wave which varles in amplitude in acc'or ance with thewave form of a signal to be transmitted.

It is well known that a wave of the high f modulated in accordance withthe signal frequency a, where a is the instantaneous' value of thesignal frequency, may be considered as composed of three componentshaving the frequencies f, f-I-a: and f-a. Considerable power is wastedin radiating the unmodulated component of frequency f, and it isdesirable for efficient transmission to radiate only the pure modulatedwaves of frequencies f-l-a and f-a, the unmodulated component beingrestored in any suitable manner at the receiving station..

An object of the 'present invention is to provide a modulating systemfor transmitting a pure modulated wave.

The invention makes use of reactance modulators of the transformer typefor controlling the high frequency out put by varying the mutualinductance between the primary and secondary windin s of the transformerin accordance with a signal to be transmitted. The amplitude of the highfrequency currents radiated depends upon the coupliny between theprimary and secondary windings and by varying this coupling, i. e., themutual inductance, in accordance with the signal, a vmodulation of thecarrier wave is effected. The variation in coupling is effected byvarying the permeabilities of the transformer cores in accordance withthe signal currents.' The secondary windings of the two transformers areconnected to the antenna in opposition to each other, so that no highfrequencyt power is radiated in the absence of signalin currents. Theeffect of signaling currents 1s to increase the permeability'of onetransformer core, and to decrease the permeabillty of the other trans-.former core. This disturbs the balance of the opposed secondarywindings, and modulated high frequency power is radiated.

former has three similar components with the same frequencies. The twoopposed unmodulated components of frequency f are not varied inamplitude by the signal current of frequency a, and these components arealways balanced out so that no unmodulated power is transmitted. Thepure modulated waves of frequencies f-l-a and f-a. developed in thetransformers by the signal currents, agree in phase and so reinforceeach other.

Another object of the invention is to prevent the induction of radiofrequency currents in the excitation winding. This is accomplished byproviding two paths in opposition for the high frequenc flux, theexcitation winding being linke by both fluxes so that the effect of theopposed fluxes is to induce no resultant E. M. F in the excitationwinding.

A source of steady current is used to bring the permeability of thecores to the desired point about which the permeability is changed bythe signaling currents,

A further object of the invention is to use a single excitation windingfor each transformer, which is to be supplied by both the steady sourceand `the signallng source, the

currents from these sources aiding in one winding and opposing in theother, and to prevent the currents supplied by each source from beingshort-circuited through the other source. To this end the inventionprovides an impedance coil in circuit with the steady source and acondenser in circuit with the signaling source. The steady currentcannot traverse the condenser, while the variable signaling currentscannot pass through the impedance coil, so that both currents areproperly supplied to the single excitation winding.

It has been determined that best results are obtained when themodulators are energized by a nerator which acts as a pure resistance.lil order to provide such a generator the reactance of the same isneutralized by a reactance of opposite characteristics. For instance, ifthe generator has lnductance, then a capacity is provided to neutralizethe inductance of the generator which accordingly acts as a pureresistance.

For further details of the invention reference may be made to thedrawings, in Which- Figs. 1, 2 and 3 show diagrammatically systemsembodying the invention.

In Fig. 1 the reactance modulators or transformers3 and 4 are connectedbetween the source of radio currents 5 and the antenna 6. Thetransformer 3 has a toroidal core 7 with the crossbar 8. Disposed on thetoroidal core 7 at either side of the crossbar 8 are the two halves 9and 10 of the primary winding. The secondary windings 11 and 12 aresimilarly disposed on either side of the cross bar 8. The transformer 4also has a toroidal core 13 with a crossbar 14, and a similar divisionof the primary windings 15 and 16, which are in circuit with the highfrequency source 5 and the'primary windings 9 and 10. The secondarywindings 17 and 18 are disposed half on either side of the crossbar 14,and are connected in opposition to the secondary windings 11 and 12. Thesecondary windings 11 and 12, 17 and 18, are in circuit with the antenna6, which is tuned by means of the induetance 19 to the frequency to beradiated which may be one or both of the side frequencies f-l-a, f-a.The circuit including the primary windings and condenser 20 is tuned tothel frequency supplied by the source( 5 by means of the condenser 20which is variable. As explained above it has been determined that formaximum sensitiveness the generator 5 should act as a pure resistance.If the generator 5 has inductance, then means, such as condenser 50, isprovided to counterbalance its inductance. If the generator 5 had anequivalent capacity then the element 50 should be an inductance.

In order to bring the permeabilities of the cores 7 and 13 to a desiredpoint, the excitation winding 21, arranged on cross bar 8, and theexcitation winding 22 upon the crossbar 14 are supplied through theadjustable rheostats 23 and 24 from a source of steady current 25. Inorder to vary the permeabilities of the cores 7 and 13 in accordancewith a signal to be transmitted, the winding 26 on crossbar 8 and thewinding 27 on crossbar 14 are connected through transformer 28 to thesignaling device 29. It will be noted that the core 7 and crossbar 8provide parallel magnetic paths, the primary and secondary windingsbeing disposed artly in each path and the windings 21, 26 eing common toboth paths. lf the coils 21 and 22 are so connected to the battery 25 asto supply fluxes in the same direction, as shown in the drawings, thenthe flux from the winding 2-6 will oppose the flux produced by winding21 at the instant that the flux produced by winding 27 is aiding the Huxproduced by winding 22. In

the drawings, the relative direction of the fluxes is shown by arrows,each arrow indicating the direction of the flux produced by the windingenclosing that arrow. When there are no signaling currents no highfrequency power will be radiated, as the secondar'y windings ofthe twotransformers are balanced in opposition. When signaling currents aresupplied to the transformers, the differential action of the windings 26and 27 produces additive effects in the secondary circuit, so that amodulated wave is transmitted by the antenna system. As explained above`the unmodulated components supplied by the two transformers are balancedout and only a pure modulated wave is transmitted. Since the primary andsecondary windings are equally distributed at each side p of thecrossbar, the high frequency flux takes a circular path through thetoroidal core and none of the hie-h frequency flux traverses thecrossbar. sidered that the high frequency fluxes do traverse thecrossbar 8 but traverse it in opposite directions so that noresultantelectromotive force is induced in the excitation windings. Thismakes it unnecessary to insulate the windings 21, 22, 26 and 27 for highvoltage high frequency electromotive forces which might otherwise bcinduced in these windings by the high frequency flux.

In Fig. 2 the signaling currents supplied by the signaling device 30may, if desired, be amplified by one or more amplifiers 31 of the audiontype. Instead of using four windings on the crossbars of the twotransformers as in Fig. 1, only two windings 32 and 33 are used in thesystem of AF ig. 2. The steady current for the windings 32 and 33 issupplied b v the battery 34, one terminal 35 of which is connected t0terminal 36 of winding 32 and to terminal 37 of winding 33. The otherterminal 38 of the battery is connected through rheostat 39 and animpedance coil 40 to the other terminal 41 of winding 32. Terminal 38 ofthe battery is also connected through rheostat 42 and impedance coil 43to the other terminal 44 of winding 33. Signaling currents are suppliedby the transformer 45 over the lines, 46 and 47 to the terminals 41 and44, respectively. ln the lines 46 and 47 are connected condenscrs 48 and49 respectively to prevent currents supplied by t e battery 34 fromtraversing the secondary winding of transformer 45. The currentssupplied by the signaling source and the battery 34 produce fluxes inthe crossbars 32 and 33 which are additive in one of these crossbars anddifferential in the other, as is the case in Fig. 1. The impedance r itmay be-conlll) lll)

l'll) coils 40 and 43 .prevent the signaling cur- The condensers 48, 49insure that the secondary winding of transformer 45 will notshort-circuit the windings 32, 33 for direct current from battery 34;.and the impedances 40. 43 prevent the lines including the resistanees 39and 42 from short-eircuiting the windings 32, 33 as to signalingcurrents.

The transmission of a pure modulated wave by the system of Fig. 2 iseffected in the sairie manner as explained in connection with Fig. l.

In the system shown in Fig. 3, the transformer cores of Fig. 2 arereplaced by the four toroidal cores 51, 52, 53 and 54.

The arrows in Fig. 1 show the opposing magnetic paths provided by theunitary cores in Figs. 1 and 2. In Fig. 3 each high frequency flux pathis provided in a separate core, the primary and secondary windings beingdisposed in these paths as before and the excitation windings 32 and 33each encircling two high frequency paths for opposed fluxes, so that nohigh frequency E. M. F. is induced in the excitation windings. Thearrangement of cores in Fig. 3 has the advantage that the primary,secondary and excitation windings may be uniformly distributed abouttheir cores.

In regard to all of the figures, the resonance of the local circuitincluding the condenser 20 and the primary windings of the transformers.is effected by` the inductive relation of the primary to the secondarywindingsl This inductive relation depends upon the variablepermeabilities of the cores which ar@ controlled by the signalingcurrents. rPhe variable condenser 20 is so adjusted, when the signalingcurrents are zero, that the local circuit including the condenser 20 andthe primary windings of the transformers is timed to the frequencysupplied hy the carrier current generator 5. Since the primary windings9, 10. 15. 1G and the condenser 20 are in shunt to generator 5 and arctuned to the frequency supplied by generator 5. the windings 9. 10, 15,16 and condenser Q0 form a path which. except for the effect of itsresistance component, offers infinite impedance to currents of thecarrier frequency, The closed oscillation circuit 9,v

10, 15, 1G is accordingly termed a loopresonant circuit and it is opaqueto currents of the carrier frequency. The circuit 9, 10, 15. 16 beingtimed as described, insures that no power except the negligible amountnecessary to supply the RP and core loss will be drawn from thegenerator 5 when the signaling currents are Zero, which is of advantageas it prevents a waste of the high frequency power. The effect ofsignaling currents however is to vary the inductance in the circuit 9,10, 15, 1G, 20 which disturbs and upsets the resonance condition of theloop-resonant circuit and draws more' or less power from the generator 5in accordance with the signaling currents.` As illustrating one of themodifications that may be made in the systems shown, it may be mentionedthat in Fig. 1, for instance, transformer 4 may be dispensed with and anordinary transformer or alito transformer may be substituted therefor.This amounts to iiiductively relating the primary coils 15, 16 to thesecondary coils 17, 18 in the usual manner, the coils 27 and 22 beingdispensed with so that transformer 28 supplies only coil 2G and battery25 furnishes current only to coil 21.

Although this invention has been illustrated and described in connectionwith radio signaling, it is to be understood that it is applicableaswell to transmission of energy waves over conducting circuits.

What is claimed is:

1. The combination of a source of high frequency currents, a line'selectively responsive to modulated currents of said high frequency,means associated with said source and said line for modulating said highfrequency currents,said means comprising two transformers having primarywindings connected to said source and secondary windings connected inseries opposition in said line, and signaling means for differentiallycontrolling said transformers whereby a pure modulated wave istransmitted by said line. c

2. The combination of two transformers each having niagnetizable meanswith primary -and secondary windings thereon, a source of high frequencycurrents for supplying said primary windings. a line selectivelyresponsive to modulated currents of said high frequency associated withsaid secondary windings, said secondary windings being balanced inopposition and connected in series in said line to normally restrain thetransmission of energy from said source to said line, and signalingmeans controlling said magnetizable means for disturbing the balancedcondition of said windings whcreby said high frequency currents aremodulated in accordance with the signal to he transmitted.

A signaling system comprising a source of high frequency currents. aline selectively responsive to modulated currents of said highfrequency, means between said source and said line for modulating saidhigh frequency currents, said means comprising two transformers havingprimary windings connected to said source and secondary windingsbalanced in opposition in said line, and signaling means fordifferentially controlling said transformers whereby a pure modulatedwave is transmitted.

4. In a signaling system, a high frequency circuit including a source ofhigh frequency current and magnetic control means in series therewith insaid circuit, an excitation winding for said control means, a source forsupplying a steady current to said winding, a source of signalingcurrent for said winding, means for preventing said signaling currentfrom passing through said first mentioned source, and means forpreventing said steady current from passing through said signalingsource.

5. ln a, signaling system, a high frequency circuit including a sourceof high frequency current and magnetic control means in series therewithin said circuit, an excitation winding for said control means` a sourcefor supplying a steady current to said winding, a

' source of signaling current for said winding,

an impedance coil for preventing said signaling current from passingthrough said first mentioned source, and condensive reactance forpreventing said steady current from passing through said signalingsource.

6. ln a system for the modulation of high frequency currents, thecombination of two excitation windings, a source for supplying a steadycurrent to said windings` means for independently adjusting the currentin each ofusaid windings. a. source of signaling current for supplyingsaid windings-` lmeans for preventing said signaling current frompassing througlL said first mentioned source, and means for preventingsaid steady current from passing through said signaling source.

7. A signaling system comprising two excitation windings, a source ofcurrent. for supplying said windings, an impedance coil anda rheostat incircuit with each of said windings, a source of signaling current forsupplying said windings. leads for connecting said signaling source tosaid windings, and a condenser in each of said leads, the currents fromsaid sources aiding in one of said windings and opposing in the other ofsaid windings.

8. In a signaling system, a modulator consisting of two transformersbalanced in opposition each transformer comprising primary and secondarywindings and magnetizable means providing two magnetic pat-hs, saidprimary and said secondary windings be- .ing disposed part in one ofsaid paths and part in another of said paths. an excitation windingdisposed about a common portion of said paths a source of alternatingcurrent to be modulated connected to said primary winding and atransmission circuit tuned to the frequency of said modulatedalternating current connected to said secondary winding.

9. In a signaling system. a modulator consisting of two transformersbalanced in opposition each transformer comprising primary and secondarywindings and magnetizable means, and an excitation winding for varyingthe permeability of said magnetizable means, a source of alternatingcurrent to be modulated connected to said primary Winding, a source ofcurrent for said excitation Winding, said excitation winding being sodisposed as to prevent the same from becoming a source of currents ofthe frequency supplied to said primary winding and a translation circuitconnected to the secondary windings and tuned to the frequency of themodulated alternating current.

10. A modulating system comprising a source of unmodulated oscillationsand means for modulating said oscillations in accordance with signalsincluding a reactance conductor in series with said source for supplyingenergy to a line, and means in shunt to said conductor having areactance equal in value but opposite in kind to that of said reactanceconductor with respect to oscillations of the frequency supplied b vsaid source.

l1. A reactance modulator comprising a line, a high frequency circuit,magnetic means connecting said line and said circuit, an oscillationgenerator connected to said high frequency circuit, said line beingtuned to a frequency differing by approximately mean speech frequencyfrom that of the oscillations produced by said generator and signalingmeans for varying the impedance which said high frequency circuit offersto said generator.

12. An oscillation generator, and a series circuit connected theretocomprising means having a reactance equal in value and opposite in kindto the reactance of said generator, a closed loop circuit tuned to thefre- 'quency of said generator and a work circuit arranged to besupplied with current from said loop circuit.

13. A signaling system comprising means for supplying high frequencyoscillations, a modulator having primary and secondary windingsassociated with a core of magnetic material, said primary windings beingadapted to be energized by said means and a high frequency line fortransmitting modulated currents of the carrier frequency supplied bysaid means and adapted to be energized by said secondary windings, acondenser in series with said means, and another condenser in shunt tosaid primary windings.

14. In a signaling system for transmitting a pure modulated wave, atransformer comprising primary and secondary windings and magnetizablemeans having two magnetic paths, said primary and said secondarywindings being disposed part in one of said paths and p art in anotherof vsaid paths, and an excitation winding common to both of said paths.a similar transformer, a signaling device in circuit with the excitationwindings of said transformers, a source of high frequency currents forthe primary windings of said transformers` the secondary windings of oneof said transformers being connected in opposition to the secondarywindings of the other of said transformers, and a high frequenc lineadapted to be supplied by said secon ary windings.

15. The combination of a source of high frequency oscillations, a linetuned to a frequency differing by approximately mean speech frequencyfrom that of said oscillations and two reactance devices havingprimarywindings connected to said source, and secondary windingsbalanced in series opposition in said line.

16. The combination of two transformers each having primary, secondaryand excitation windings, a generator of carrier waves for supplying saidprimary windings, a source of steady current and a source of signalingcurrent for supplying said excitation windings, a high fre uency lineadapted to be differentially supp ied by said secondary windings, andmeans for tuning said high frequency line to a frequency differing fromthat of said carrier waves by the frequency of said signaling current.

17. The combination of two transformers eacli having primary, secondaryland excitation windings, a generator of carrier waves, means forneutralizing the reactance of said generator, said generator being incircuit with said primary windings, tuning means associated with saidprimary windings, a source of direct current for supplying saidexcitation windings, signaling means for controlling the inductiverelation of said primary to said secondary windings, a .high frequencyline adapted to be. differentially supplied by said secondary windings,and means for tuning said line to the frequency to be transmitted.

18. The combination of a carrier current generator, a modulatorcomprising a condenser and primary windings in series circuit with saidgenerator, secondary windings associated with said primary windings andconnected in series opposition, signaling means controlling theinductive relation of said primary and secondary windings, and a highfrequency circuit connected to said secondary windings to receivemodulated carrier current energy therefrom and tune-d to one of theprincipal frequencies of said modulated carrier current.

19. The combination of a high frequency generator, a condenser andprimary windings in series circuit therewith, secondary windingsinductively associated with said primary windings, signaling windingsassociated with said primary and secondary windings to producemodulation of the current supplied by said primary windings to saidsecondary windings, and a high frequency circuit tuned to a principalfrequency of said modulated current connected to said secondarywindings.

20. The combination of a high frequency generator, a condenser andprimary windings quency from that of sai carrier current, the

.secondary windings of said transformers being connected in oppositionto said line.

22. In a signaling system for transmitting a pure modulated wave, twotransformers each .comprising primary and secondary windings, a sourceof carrier frequency currents forthe primar windings of saidtransformers, a line tune to a frequency differing by approximately meanspeech frequency from that of said carrier current, the secondarywindings of said transformer being connected in opposition to said line,and means for controlling the energy which said transformers transfer tosaid line.

23. In a signaling system the combination of asource of high frequencyoscillations, a transmission circuit, a magnetic modulator connectingsaid source to said circuit, and means conductively connected to saidsource for preventin substantially any current flow from sai sourceduring non-signaling periods.

24. The method of variably controlling the transmission of analternating current from a source to a utilization circuit whichcomprises subjecting rthe current flowing from said source to theimpedance offered by a loop-resonant circuit and varying the impedanceoffered to said current by said loop resonant circuit in accordance withsignals and in such manner that the impedance offered by saidloop-resonant circuit is a maximum at the instants of minimumtransmitted current.

25. A source of high frequency current, a circuit directly ccnnectedthereto and containing a closed loop having inductive react- -ance andcapacity reactance so proportioned as to offer substantially infiniteimpedance in said circuit to current from said source, a source ofmodulating waves, an outgoing circuit containing impedance and arrangedto be normally substantially out of effective energy transfer relationwith said loop, and means for setting up effective energy transferrelation between said loop and said outgoing circuit in accordance withthe instantaneous amplitudes of said modulating waves.

26. A source of high frequency currents,

lll

a circuit connected thereto and containing a. parallel branched pathwhich oil'ers substantially infinite impedance to the current from saidsource, a source of modulating waves coupled to one branch of said. pathto vary the impedance of said circuit 1n accordancc with variations ofsaid modulatlng waves and an outgoing circuit coupled to one branch ofsaid path in a manner to have large amplitude current impressed thereonat the instants when the impedance of said patli is of relatively smallamplitude and vice versa.

2T. In a modulating system, a source of oscillations to be modulated, acapacity and an inductance connected to said source in parallel witheach other to form a loop-resonant circuit tuned to the frequency ot'said source, said inductance being comprisedln two parts, a pair ofseparate windings inductively related respectively to the two parts ofsaid inductance and connected 1n opposition in an outgoing circuit, andmeans for simultaneously varying the mutual inductance between eachportion of said inductance and its inductively related Winding inaccordance with signals to be transmitted. 28. In a modulating system, asource ot' sustained oscillations possessing reactance, a reactiveelement of opposite kind to the reactance of said source and of amagnitude to neutralize the reactance of saidsource, an inductance and acapacity connected in parallel with each other and connected to saidsource and reactive element 1n series, said inductance and capacitytogether forming an anti-resonant circuit to the oscillations from saidsource, said inductance being comprised in separate portions, acorresponding number ot' windings each inductively related to adifferent one of said inductance portions and connected in an outgoingcircuit to normally apply respectively opposlte potentials to saidcircuit, whereby when no signals are being sent substantially nooscillations from said source reach said outgoing circuit, and means forsimultaneously Varying the mutual inductance between each of saidinductance portions and its associated winding to vary in opposite scusethe oppositely applied potentials to said outgoing circuit in accordancewith signals to be sent.

29. In a modulating system comprising a generator of oscillations and anoutgoing circuit, means for preventing transmission of the oscillationsto said circuit during nonsignaling periods comprising a pair oftransformers having primary windings con nected to said generator andsecondary windings connected in said outgoing circuit in opposition toeach other, means for reducing the load drawn from said generator duringnon-signaling periods comprising a capacity in shunt of said primarywindings and forming with said transformer inductanccs a loop-resonantcircuit of very high impedance to the oscillations from said generator,and means to vary the mutual inductance ot' at least one of saidtransformers in accordance with signals.

30. In a modulating system, a source of oscillations, an outgoingcircuit having impedance, a, loop-resonant circuit connected to saidsource and offering substantially infinite impedance to the oscillationsfrom said source during non-signaling periods, said loop-resonantcircuit having substantially zero net Inutual inductive Arelation withsaid outgoing circuit, and means acting in response to impressed signalsfor setting up a net mutual inductive relation between saidloop-resonant and said outgoing circuit to an extent substantiallyproportional to the instantaneous amplitudes of the signals, whereby theimpedance offered by said loopresonant circuit to oscillations from saidsource is decreased and signal modulated oscillations are impressed onsaid outgoing circuit.

In witness whereof, I hereunto subscribe Amy name this 29th day ofDecember A. D.

RALPH V. L. HARTLEY.

